Airplane rib



1939. KfscI-IMIDT AIRPLANE am Filed March 9, 1938 3 Sheets-Sheet 1 INVENTOR KARL SCHMIDT Aug. 1, 1939. scHmm- 2,167,686

' AIRPLANE RIB Filed March 9, 1938 5 Sheets-Sheet 2 VJFJ. as

E 7 s6 INVENTOR BY KARL SCHMIDT ATTORNEY Aug. 1, 1939. K. SCHMIDT 2,167,686

AIRPLANE'RIB Filed March 9, 1938 3 Sheets-Sheet 3 I8 23 a2 57 5a a a! 23 ca 'l-l 4s f 4a *r 4a 4| as F1 8 g '1 c7; 6? at an a:

F1 /0 ea INVENTOR Y KARL SCHMIDT ATTORNEY Patented Aug. 1, 1939 UNITED STATES PATENT OFFICE 6 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G.-'l

Thisinvention relates to airplane ribs and it has a particular relation to the capstrip portions thereof to which the envelope or covering is secured.

Heretofore it has been the practice to attach the fabric covering of an airplane wing to the capstrip of the rib member by a lacing cord looped around the capstrip and cover and knotted at intervals. In this method the fabric cover is stretched over the airfoil frame in contiguous,

relation to the capstrips of the rib members after which the usual reenforcing tape of a width equal to the capstrip is placed on the cover over the entire length of the capstrip and the two secured thereto by the lacing cord which is looped tightly around the capstrip at intervals.

The principal object of this invention is the provision of an airplane wing rib which is so constructed that the fabric covering may be attached thereto continuously throughout the entire length of .the rib, thus avoiding localized strains and insuring that the covering is stretched tightly with evenly distributed tension so that the full strength of the cover fabric may be developed.

Another object of the invention is the provision of an airplane wing rib and a cooperating cover fastening device by means of which the fabric covering, when attached to the wing, will present a smooth cambered surface of high aerodynamic emciency.

With these and other objects in view, as well as other advantages that may be incident to the use of the improvements, the invention consists in the parts and combinations thereof hereinafter set forth and claimed, and with the understanding that the several necessary elements constituting the same may be varied in proportion and arrangement without departing from the nature and scope of the invention, as defined in the appended claims. In order to make the invention more clearly understood, thereare shown in the accompanying drawings, means for carrying the invention into practical use, without limiting the improvements in their useful application to the particular construction, which, for the purpose of explanation, have been made the subject of illustration.

In the accompanying drawings:

Fig. 1 is a diagrammatic perspective view showing the method of attaching a fabric covering to the wing in accordance with the invention;

Fig. 2 is a transverse vertical sectional view through an airplane wing;

Fig. 3 is an enlarged vertical sectional view through the capstrip of the improved wing rib; and

Figs. 4 to 10 are similar views of different forms of capstrips embodying the invention.

.Referring to the drawings and particularly to Fig. 2 thereof, an airplane wing constructed in accordance with the invention is shown as comprising upper and lower capstrips l0 and II respectively, secured to fore-and-aft longitudinal beams 12 and I3 and with one another by diagonal bracing members 14. The capstrips l0 and l I may be of different cross-sectional shapes but in each case the load characteristics are substantially the same.

Fig. 3 illustrates a capstrip of substantially V- shape being formed with an in r vertical flange I5 and outer diverging flanges I terminating in inwardly extending edges ll. Theg-fabric' covering I8 is flexed into the depression formed by the flanges l8 and secured in position by a longitudinally extending relatively inflexible load-strip I9 which is secured to the capstrip 10 at intervals by screws 20. The covering I8 is preferably reenforced along its line of attachment to the rib III by interposing it betwen layers or plies of iabric 2land 22, the former disposed along the full length of the capstrip and the latter being wrapped around the load-strip. The load-strip lies wholly within the depression between the flanges and is covered by a sealing tape 23 which is dope cemented to the fabric covering [8' so as to provide a smooth flat surface of minimum wind'drag. The warp and woof of the fabric of the plies 2| and 22 preferably extends at an angle to that of the coverings so as toobtain the maximum reenforcing effect. The screws 20 are of the self-lapping type and are screwed into apertures 24 previously bored in the capstrip. The heads 25 of these screws are seated within rec'esses 26 formed in the loadestrip 19 so as to form a flush surface therewith and are formed with pointed ends 21 for entry without rupturing between the threads of the fabric when the loadstrip is secured in position.

In Fig. 4 there is shown a modified form of capstrip in which a flat bottomed channel 28 is formed along the outer edge .of the rib. This channel is of less depth than the depression shown in Fig. 3 andas a result the load-strip I9 extends a slight distance above the surface of the wing. Also, the sealing tape 23 has been omitted in this form.

In Fig. 5 there is shown another form; of the invention in which the capstrip consists of two verging outer flanges 3| terminating in inwardly extending edge portions 32. In this form of the invention the fabric covering I8 is secured to the capstrip by a load-strip 33 having diverging side portions 34 disposed at an angle corresponding to that of the flanges 3| and with an intermediate reenforcing rib 35. This rib 35 is recessed at intervals, as indicated at 36, to permit self-tapping fastening screws 31 to be inserted through openings formed in the flanges 3| and 34 of the capstrip and load-strip for engagement with tapping plates 38. As in Fig. 2 the recess in which the load-strip is secured is covered by sealing tape 23. The spacing members 30 are only located at the points along the capstrip where the load-strip is secured thereto, thus lightening the structure. This particular construction is ideally suited for the use of aluminum coated metal. After all of the parts of the capstrip have been shaped to the desired contour, they are readily assembled with the spacer plates 30 by a spot welding process.

In Fig. 6 there is shown a rib construction quite similar to that shown in Fig. 5 in principle. In this construction the inwardly. extending flange 39 of the cap-strip is a part of and built into the rib truss and is formed with an enlargement or bead 40 along its outer edge. A plate 4|, having outwardly diverging flanges 42 terminat ng in inwardly projecting edge portions 43, is secured to the flange 39 by self-tapp ng screws 44 which also secure the load-strip 45 and interposed covering I8 and reeniorcing strips 2| and 22 in position. This load-strip is the same as that shown and described in connection with Fig. 5, differing therefrom in that reenforcing rib 35 is omitted.

In Fig. '7 there is illustrated a still further modified form of the invent on wherein the capstrip comprises a metal plate bent to form an inwardly extending flange or base 46 of substantially U- shape in cross-sectionand with outwardly diverging flanges 41 which terminate in inwardly extend ng marginal edges 48. The structure may be reenforced by gusset plates 49 which are welded to the base portion 46 and flanges 41 at intervals. In this construction the fabric covering l3 and reenforcing strips 2| and 22 are secured in position by a load-strip 50 of triangular cross-section to provide a relatively wide base 5| for engagement with the fabric and a longitudinally extending reenforcing rib 52. This rib is recessed at intervals, as at 53, to receive self-tapping fastening screws 54 which are threaded into drilled openings 55 provided in inserts 56 secured at intervals within the U-shaped portion 46 of the capstrip.

In Fig. 8 there is illustrated a still further modified form of the invention but which is somewhat similar to that described in connection with Fig. 6. In this particular construction the flanges 42 are more or less flexible and are intended to deflect slightly under varying cover loads, as indicated by broken lines in this flgure. Also, the fabric cover l8 and reenforcing strips 2| and 22 are held in position under tension by means of a rectilinear loading-strip 5'! which is secured to the flange or web 39 by self-tapping screws 58. This construction is designed to facilitate and simplify the forming operations.

In Fig. 9 there is shown another form of capstrip which is much the same as the semi-flush type shown in Fig. 4 and may be fabricated by the extrusion process. In this instance the sides of the channel portion 59 are more or less flexible under variable cover loading conditions, as in the structure shown in Fig. 8. It will be noted, however, that a tapping plate 60 is employed at the points of attachment of the loading strip l9 into which the screws 20 are threaded. These tapping plates are inserted in openings 6| formed in the flange or web of the capstrip.

Whereas, the capstrip constructions hereabove described, were specifically designed to withstand negative airloads, it is apparent that such constructions are not necessarily adequately prepared to withstand positive airloading such as normally is imposed on the pressure or underside of the airfoil. When the airplane is sharply maneuvered at high speed, the maximum positive airload is much less than the developed negative pressure, and so the requirement for a suitable capstrip is somewhat difierent for the purpose.

The structure shown in Fig. 10 was particularly des gned to resist such positive airloading of the airplane cover and also for resisting negative airload ng. It will be noted that the capstrip in this figure s of substantially T-shape in cross-section being formed with an inwardly extending web 62 and a horizonal flange portion 63 terminating in rounded or inwardly curved edges 64. This form of capstrip may be fabricated by the extru-' sion process and is well fllleted at the juncture of the web and flange components, as indicated at 65. The covering l8 and reenforcing strips 2| and 22 are held in position by a loading-strip 66 havinginwardly curved edges 61 which cooperate with the edges 64 of the capstrip in drawing the cover tight and in afiordingadditional rigidity to the structure. As in the structures previously described the loading-strip 66 is secured to the capstrip by self-tapping screws 68.

With particular reference to Fig. l, the covering is applied to and stretched over the wing panel manually in such manner that the warp and woof threads extend in straight lines both longitudinally and transversely of the wing. The next operation is to depress the fabric into the grooves of the Y-shaped capstrip 0f the several ribs and to secure it in position therein by the load-strip, the described operation progressing successively from the inboard-rib toward the tip of the wing, as indicated at a, b, and "c in Fig. 1. The original tension on the fabric covering is maintained during this operation by weights W suitably arranged and attached to the marginal edges of the fabric. It will be apparent that as the loadstrips are secured in position the fabric will be drawn inwardly and elevate the weights which maintain a constant tension on the fabric. The top and bottom covers of the wing are applied in a like manner, and the leading and trailing edges of the wing are covered with thin sheet metal after which the surfaces are treated with dope to complete the wing. Other modiflcatonsand changes in the proportion and arrangement of the parts, other than those shown, may be made by those skilled in the art, without departing from the nature and scope of the invention, as deflned in the appended claims.

The invention described herein may be manufactur'ed and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim: 1. An airplane wing rib construction comprising a capstrip having an inwardly extending web portion and an outer channel portion of portion of said load-strip having a rib extending longitudinally therealong.

2. An airplane wing rib construction comprising a capstrip having an inwardly extending web portion and outwardly extending diverging flanges forming a depression, and a load-strip formed with outwardly diverging flanges attached to the diverging flanges of said capstrip for flexing a fabric wing covering into said depression and securing it under tension therein.

3. An airplane wing rib'construction comprising a capstrip having an inner web portion and a separable outer channel portion having outward- 1y diverging side flanges, and a load-strip attached to the flanges of said capstrip for flexing a fabric wing covering into said channel portion and securing it under tension therein.

4. An airplane wing rib construction comprising a capstrip having an inwardly extending web portion of substantially U-shape in cross-secaromas tions and outwardly extending diverging flanges forming a depression, inserts fixed in said U- shaped portion at intervals therealong; and a load-strip attached to said inserts for flexing a fabric wing covering into said depression and securing it under, tension therein, said load-strip having an outwardly extending rib extending longitudinally therealong.

5. An airplane wing rib construction embodying a capstrip comprising two complementary members having parallel portions secured together to form an inwardly extending web and outer diverging portions forming a channel of substantially V-shape in cross-section, and a load-strip corresponding to the shape of said channel attached to said diverging portions for flexing a fabric wing covering into said channel and securing it under tension therein.

6.'An airplane wing rib construction embodying a .capstrip comprising two complementary members having parallel portions secured together to form an inwardly extending web and outer diverging portions forming a channel of substantially V-shape in cross-section, and a load-strip having diverging flanges attached to the diverging portions of said members ior flexing a fabric wing covering into said channel and securing it under tension therein.

KARL SCHMIDT. 

